1. Field of the Invention
This disclosure pertains to a process of treating animal feed with aqueous formaldehyde which renders the feed highly resistant to recontamination by pathogenic bacteria such as Salmonella, Streptococcus, Staphylococcus, E. coli, Clostridia and Bacillus.
2. Discussion of the Background
In the early 1960's people in the field of animal husbandry were shocked to learn that toxins produced by molds growing in feedstuff had killed thousands of turkeys. This phenomenon led to twenty-five years of intensive study in private laboratories and universities on molds and the toxins they produce. By the 1980's it was generally recognized that molds in animal feedstuffs are an economic hazard as well as a health hazard to man and animal. Mold inhibitors, usually containing propionic acid, were added to animal feedstuffs to control mold growth. In 1977 few animal feed producers were using mold inhibitors in their feeds. Today most feed producers use mold inhibitors.
Given the intense study and publicity surrounding molds it is surprising, in retrospect, that no one seemed to be concerned about another member of the microbiological kingdom, bacteria. However, in the early 1980's a group of bacteria known as Salmonella was brought forcefully to the public's attention because several people, in isolated cases, died from Salmonella poisoning, i.e., by ingesting large amounts of Salmonella bacteria. Health authorities traced the causes of these Salmonella infections back to their sources and often implicated meat and eggs. Outbreaks of Salmonella poisoning recurred over the years and became a serious concern to people in many countries, especially in England and the United States. The Food and Drug Administration in the U.S.A. came under pressure from Congress to find a solution to Salmonella poisoning. The British government also pressed local authorities to solve the problem. As a result, slaughter houses were cleaned up, some were closed and thousands of hens were condemned because they were in flocks where Salmonella was found. Producers spent large amounts of money to ensure Salmonella-free produce. But instead of improving the situation, contamination by Salmonella increased. The health authorities of England publicly admitted that all their efforts had not even diminished the problem.
In 1982 scientists at Anitox Corporation began laboratory studies on Salmonella and found that the original source of contamination is usually the feedstuffs the animals eat. It was shown that very light contamination of Salmonella in feedstuffs is all that is needed to contaminate the animal. Once the animal (the use of the word animal includes all forms of livestock such as cattle, poultry, swine, fish, etc.) eats the contaminated feedstuff the bacteria multiply rapidly in the moist warm environment of the gut and feces. In fact under these ideal conditions one Salmonella bacterium can multiply to 1,000,000 bacteria in 30 hours. This increase, literally an explosion of growth, contaminates the intestinal tract, the feces, the litter, the hair, the feathers and the surrounding environment. When these animals are processed the contamination increases and so all efforts to control Salmonella by sterilizing the production facility become inadequate. Even though federally-licensed vaccines against Salmonella are available for swine, laying hens and breeders, they have had limited success controlling the problem. For instance, the chicken vaccine cannot be used in broilers or meat-type chickens due to accumulation of vaccine residues in the meat. Today it is estimated that 30% of uncooked chicken on the supermarket shelf is contaminated with Salmonella.
It would seem that it should be easy to dip a carcass in a bacteriocidal solution and kill all the Salmonella, but this is not the case because recontamination occurs quickly. Furthermore, radiation treatment, which has recently been approved by the Food & Drug Administration, will kill all bacteria on animal carcasses. But again, this technique has not solved the problem because recontamination of the carcass usually occurs prior to its consumption by the consumer.
It is now generally recognized that limiting the introduction of Salmonella through the feed is the most effective long range plan for improving the situation and many compounds with known bacteriocidal properties, such as lactic acid, propionic acid, formic acid, butyric acid, sorbic acid, benzoic acid and combinations of these have been tested. While many of these agents kill bacteria in solution, they do not kill all the bacteria in animal feedstuffs. Woolford, M. K., "Microbiological Screening of Food Preservatives, Cold Sterilants and Specific Antimicrobial Agents as Potential Silage Additives", J. Sci. Ed. Agric. 1975, 26, 229-237. To be effective against Salmonella, a bacteriocidal treatment must kill essentially all of the bacteria. Methods that kill 95% or even 99% are largely ineffective because the residual bacteria can multiply rapidly and recontaminate the feedstuff, and eventually the entire processing facility.
It is generally known that formaldehyde kills Salmonella when applied to feedstuff in large quantities. Mixtures of aliphatic acids, formaldehyde, methanol and terpenes are very effective when applied to feed by conventional spraying equipment. However, such treatments fail to eliminate the Salmonella effectively when too little formaldehyde is used or when the solution is not sprayed uniformly onto the feedstuff, thereby allowing some small number of bacteria to survive and multiply.
We have developed an improved process for applying formaldehyde to feed in significantly lower doses yet still kill essentially all the Salmonella, and in addition, the process kills virtually all other pathogenic bacteria in animal feedstuffs. The process involves applying aqueous formaldehyde onto the feed in a mist or atomized spray while mixing the feed components in a manner that ensures uniform production of a chemical adduct between formaldehyde and the feed. We have found that formaldehyde-treated feedstuffs of the present invention resist recontamination long after the formaldehyde itself has dissipated, up to 60 days or more This bacterial resistance is correlated with the quantity and uniformity of distribution of a hydrolyzable formaldehyde adduct which can be readily recovered from the feed and measured. The more evenly distributed this adduct is, the more resistant to recontamination the feed is. Bacterial resistance is important because conventional feedstuffs are usually contaminated during transport and storage under the usual inadequate sanitary conditions. Feed generally becomes recontaminated during transport by passing through contaminated feed-handling equipment, such as augers, elevators, drag lines, bagging equipment and trucks. In storage, feed can become recontaminated by storage bins or by contact with dust, insects, rodents, birds and other animals. The quantity of bacteria capable of contaminating the feed may vary from less than 1 colony per gram, up to numerous colonies per gram of feed. It is very difficult to keep the animals healthy when they are eating contaminated feed. The present invention will change the way animals are fed, improve the health of animals, have a favorable economic impact on the animal producers and provide a cleaner, healthier meat for the consumer.
Animal feedstuffs are universally contaminated with many different pathogenic bacteria--a fact not heretofore commonly known by producers of meat, eggs and milk. We have analyzed feeds from North America, Europe, Asia and South America and found them to contain pathogenic bacteria, most commonly Streptococcus, Staphylococcus, Salmonella and E. coli. This fact seems to explain why producers find it necessary to include maintenance doses of antibiotics and other drugs in animal feeds to control Streptococcus and Staphylococcus infections in the animals and to increase yields of meat. However, the use of drugs in meat production is becoming controversial and highly objectionable to consumers. Therefore, a method of reducing disease, increasing feed conversion and yield of meat without administering antimicrobial drugs to the animal is needed. We have found that when animals are raised on formaldehyde-treated feed they thrive without maintenance doses of several antimicrobial drugs, and since they are healthier, they have little need for chemotherapeutics of any kind. In contrast, conventional feeds which have been treated with steam and pelletized do not resist recontamination. Therefore, steam treated pelletized feeds are a major cause of Streptococcus and Staphylococcus infections in livestock. Maintenance doses of several antimicrobials--both antibiotics and mycotic agents, are generally required in conventional pelletized feed to keep the animals healthy. We have discovered that formaldehyde treatment not only kills all types of pathogenic bacteria, but that the resulting feed has an unexpected property. It reduces or eliminates the need to routinely administer many drugs, particularly antibiotics, to livestock through feed. Producers have traditionally used maintenance doses of certain drugs, such as mycostatin, chlortetracycline, furazolidone, bacitracin and dimetridazole, to provide a growth advantage, in terms of feed conversion. A complete list of feed additives allowed by the FDA, grouped by their nutritional and medicinal use by species, is found in the Feed Additive Compendium, Miller Publishing Co., Minneapolis, Minn. However, by feeding the animals a diet consisting essentially of formaldehyde-treated feedstuffs, it is now possible to completely eliminate some drugs and reduce the dosage of others without suffering a loss in feed conversion. In most cases feed conversion can be increased by a combination of formaldehyde-treated feed and continued use of one antimicrobial, such as-chlortetracycline, without others.
In Europe and the United States there is growing concern over the use of antibiotic and mycotic agents in animal production for two reasons. The first concern is that most of these medicines contaminate the tissues of the animals and are consumed by humans when they eat the meat; a second concern is that pathogenic bacteria growing in animals soon develop resistance to the types of antibiotics that were used in the feed, which means that when these bacteria infect humans through contaminated meat, antibiotics which are normally effective in humans frequently fail to kill the resistant bacteria. Some antibiotics have already been banned for use in animal feed in certain places to prevent the inevitable emergence of antibiotic-resistant strains of Streptococcus, Staphylococcus, Salmonella and E. coli. It is anticipated that within a few years most antibiotics currently in use will be banned. One embodiment of the present invention eliminates the growth advantage, in terms of feed conversion, provided by maintenance doses of many drugs commonly used in animal husbandry and will be welcomed by the meat producer and public alike because the method leaves no residue in tissue, eggs or milk.
Both liquid solutions and gaseous formaldehyde are known to kill bacteria, Melhus, E. I. et al, "The Fungicidal Action of Formaldehyde", (Research Bulletin, No. 59, August 1920, Agricultural Experimental Station, Iowa State College of Agriculture and Mechanic Arts, Ames, Iowa). It is used as a fumigant (H. P. van Ekelenburg, Misset-World Poultry, Vol. 7, 28, 1991 and F. K. Wills-, Poultry Digest, 452, September 1992). An aqueous solution of formaldehyde, formic acid, methanol and sugar, preferably molasses, has been used for preserving ruminant feed, as described in U.S. Pat. No. 4,772,481. However, the viscosity of the solution is high, due to the presence of 23% to 74% by weight sugar solids. Solutions having high viscosity are not generally useful in the present method of producing formaldehyde-treated feedstuffs because it is critically important to form a mist of the solution, which is only practical if the solution has relatively low viscosity. The use of aqueous formaldehyde to destroy pathogenic bacteria in livestock waste is disclosed in U.S. Pat. No. 4,349,572 and 3,919,433. The treated excreta is useful as a feed supplement, however, the resulting feed is not highly resistant to recontamination.
We have observed that formaldehyde reacts reversibly with feedstuffs to produce a hydrolyzable adduct, and that formaldehyde-treated feed will resist bacterial growth long after the formaldehyde has been removed. One aspect of this invention is a method of applying aqueous formaldehyde to feed which maximizes bacterial resistance while greatly minimizing the effective amount of formaldehyde. When sprayed in a fine mist on animal feedstuffs, aqueous formaldehyde produces a uniformly distributed adduct that can be recovered by acid hydrolysis.
If the feed is kept relatively dry it will resist contamination under aerobic conditions for 30-45 days and in some cases 60 days or more, depending on the quantity and uniformity of distribution of formaldehyde adduct. These parameters can be measured by hydrolyzing the adduct under acidic conditions and recovering formaldehyde. The feeds of the present invention are novel and have the unexpected property of being more resistant to contamination by pathogenic bacteria than previously available feeds, even those treated with much more aqueous formaldehyde, i.e., where the solution is applied by conventional spraying equipment. The present invention can be used to produce a healthier animal and a more wholesome meat for the consumer at reduced cost.